As is generally known, there have been proposed and developed electric motor control devices configured to estimate or derive longitudinal forces of respective driving wheels from a yaw rate of a vehicle, and also configured to estimate, based on the derived longitudinal forces, a current value of electric current being supplied to each of the electric motors, even when an electric motor torque for driving each of the driving wheels becomes undetectable. One such electric motor control device has been disclosed in Patent document 1. In this prior-art electric motor control device, it is possible to evaluate, based on the estimated electric current values, the presence or absence of abnormal motor torque generated at the electric motors.
However, in order to evaluate the presence or absence of the abnormal motor torque on the basis of the longitudinal forces estimated based on the vehicular yaw rate as previously discussed, the device requires a parameter such as a lateral force acting on the vehicle. Generally, the accuracy of modeling of a tire model is not so good, and hence it is difficult to more precisely derive or estimate a parameter such as a lateral force. For the reasons discussed above, in the case of evaluation of the presence or absence of abnormal motor torque, while utilizing a parameter such as a lateral force, there is a problem that the accuracy of evaluation is lowered. In addition to the above, there is a considerable delay time until the occurrence of a lateral force acting on the vehicle, and thus an evaluation time tends to lengthen. Hence, there is a risk of the delay of the correspondence for the poor behavior, such as undesirable torque-down, occurring owing to the occurrence of abnormal motor torque.
It is, therefore, in view of the previously-described drawbacks of the prior art, an object of the invention to provide an abnormal torque evaluation apparatus for an electrically driven vehicle enabling high-precision evaluation of the presence or absence of the occurrence of abnormal motor torque of electric motors that independently drive left and right driving wheels of at least one of a front road wheel pair and a rear road wheel pair, in a short evaluation time.